The common fleas that bite humans are the dog and cat fleas (Ctenocephalides species) and the rat flea (Xenopsylla cheopis). Fleas transmit plague, murine typhus, typhus like illness due to Rickettsia felis, the rat and dog tapeworms, and Bartonella henselae. The human flea (Pulex irritans) infests human bedding and furniture but mainly in relatively humid buildings that lack central heating. Those persons who are sensitized develop symptoms such as urticaria, pruritic papules and occasionally vesicles and bacterial super infection at the site of the bite. The rat flea, X. cheopis is the most efficient vector of plague, but other fleas too may transmit the infection X.astia, X brasiliensis and Pulex irritans (human flea). Both sexes of the flea are known to transmit plague. It is a zoonoses and is basically caused by Y. pestis. It is a highly communicable disease. Since ages plague has been a great epidemic threat to nations. Y. pestis is a Gram negative bacillus and is transmitted to man by infected rodents, fleas and case of pneumonic plague itself. Plague is spread by the rat flea which dwells on rats and when such a flea bites a human.
Types of plague: Bubonic plague which is the most common form of plague. The rat flea inoculates bacilli into the human. Symptoms include regional lymphadenopathy, fever and chills, headache, prostration, painful lymphadenitis. Enlarged tender large nodes develop in the groin or axilla or neck. Pneumonic plague is highly infectious and spreads from man to man by droplet infection. Septicaemic plague is rather rare.
Flea index: It is useful for measurements of the density of fleas. It is also useful to ensure effectiveness of disinfectant spraying programme. Indices used are:
Total flea Index: it is the average number of all species per rat.
Cheopis Index: It is the average number of X. cheopis per rat. It is a specific flea index, more significant than the total flea index. If this index is more than one it is an indicator of a potentially explosive situation.
Specific percentage of fleas: it is the percentage of different species of fleas that are found on rats.
Burrow Index: It is the average number of free living fleas per species per rodent burrow.
These indices themselves do not indicate and imminent plague epidemic. They serve a warning that more stringent control measures are necessary to protect human population.
Measure to control spread of fleas: The most effective method to decrease the number of human flea bites is to break the chain of transmission from rodent to flea and then to men. This is best done by proper application of an effective insecticide. Proper susceptibility tests must be carried out to decide the most effective insecticide. DDT and BHC dusts containing 10% and 3% of the active ingredient respectively must be used. In areas where resistance to one or both of the insecticides are known, dusts of carbaryl 2% or malathion 5% will be effective. Spraying must be done inside the houses covering the entire floor area, bottoms of all walls up to 3 feet above floor level, back of the doors, roofing of the thatched houses, and crevices of the walls. Within 48 hours of application the flea index should drop down to zero. Only then will the number of human flea bites reduce and so will the spread of illness.
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